BLAME the Indian Ocean for Australia鈥檚 鈥淏ig Dry鈥� 鈥� the intense drought that has dried out much of the Murray-Darling river system, devastated agriculture and led to water rationing in Melbourne.
Until now, the Big Dry and two other major droughts to hit south-east Australia 鈥� the Federation Drought from 1895 to 1902 and the second-world-war drought 鈥� have been blamed on the El Ni帽o Southern Oscillation (ENSO), which is a cyclical change in sea surface temperatures in the tropical eastern Pacific Ocean. But when of the University of New South Wales in Sydney and colleagues compared records from 1880 to 2006 of rainfall, land temperature and drought during the June to October winter rainy period with conditions in the Indian and Pacific oceans, they found otherwise.
They found strong correlations between drought in south-east Australia and a system equivalent to ENSO in the Indian Ocean, called the Indian Ocean Dipole (IOD). 鈥淒rought wasn鈥檛 associated with ENSO events,鈥� says Ummenhofer, but instead with the absence of so-called negative events in the Indian Ocean.
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The finding makes sense because during negative IOD events, sea surface temperature rises around Indonesia and falls around east Africa, causing moisture-laden air to move across south-east Australia (Geophysical Research Letters, , in press).